A transmission is the link in the automotive drive train which conducts torque from the engine to the differential that drives the wheels on most vehicles. During the useful life of the vehicle, the transmission may malfunction due to a clogged fluid pathway, a broken rotor, a stripped gear or for some other reason, necessitating repair of the transmission. Most automotive transmissions have access openings at the undersides of their housings. These openings are normally covered by pans or covers bolted to the undersides of the transmission housings. Once a vehicle is raised from the floor on a hydraulic lift, a mechanic standing under the vehicle can remove the pan and inspect the interior of the transmission.
However, as a practical matter, major repairs to the transmission cannot be made via that inspection opening. Rather, to effect such repairs, the transmission must be decoupled from the remainder of the drive train and brought down to floor level where it can be disassembled. In the meantime, a replacement transmission may be installed in the vehicle to minimize the downtime of the vehicle.
Due to its weight, which can be 250 pounds or more, the typical transmission has to be supported mechanically during its removal and replacement. Usually, such support is provided by a lift jack which is a tool having a base which rests on the floor and a platform which can be raised relative to the base by means of a hydraulic piston, lead screw or the like. After the vehicle is raised above the floor, the jack can be positioned under the vehicle and the jack's lift platform raised so that the platform engages under the transmission. With the jack supporting the weight of the transmission, the transmission can be disconnected relatively easily from the engine, lowered and wheeled from under the vehicle. That procedure is reversed when a replacement transmission is being installed in the vehicle.
In order to prevent the transmission from falling off the jack, usually some means are provided for securing the transmission to the jack's lift platform. In the past, such means have included chains wrapped around the transmission and secured to the platform and various brackets and adaptors mounted to the platform for cradling the transmission. Examples of such adaptors are shown in U.S. Pat. Nos. 2,838,278; 3,136,526; 4,549,722 and 4,787,600. Such adaptors work reasonably well with older transmissions because the undersides of those transmissions are fairly flat and regular. That is, an older transmission has a flat area around the access opening into the transmission housing. The pan which covers that opening is also flat, generally rectangular and relatively shallow, e.g. 2 inches deep. The pan, which has a peripheral flange bolted to the housing, thus forms a flat pedestal upon which the transmission may stand in reasonably good balance. For this reason, it is relatively easy to support an old-style transmission using a conventional jack fitted with transmission adaptors of the types shown in the above patents.
In the last few years, however, the shapes of many transmissions have changed drastically due to the increased complexity of those mechanisms. This is particularly true in the case of the heavier transmissions used in trucks. These newer transmissions do not have flat areas at the undersides of the transmission housings. On the contrary, the housing undersides are rounded and the pans which cover the access openings into the transmissions are made of relatively thin gauge metal and they are deeply dished, extending 5 inches or more below the transmission housing, so that they cannot bear the weight of, or stably support, the transmissions.
For the same reasons, conventional lift jacks and the transmission adaptors therefor are not able to cradle the newer transmissions in a stable and secure fashion because they are not shaped and arranged to accommodate the pronounced curves and bulges present at the undersides of the transmissions or the unbalanced weight distributions of the transmissions. As a result, great care must be taken to make sure that a transmission does not fall off the lift jack or unbalance the jack to such an extent that the jack tips over. This requirement for extra care slows down the transmission removal and replacement process and thus increases the overall cost of transmission repair. Also, since the transmissions are not supported as stably and securely as they should be, there is an increased risk of injury to the mechanic working on the transmission.